The present invention relates to a coordinated brake control system of a hybrid brake system having two kinds of brake apparatuses.
U.S. Pat. No. 6244674 (≈Japanese Patent Provisional Publication No. 11-98609) discloses a coordinated brake control system for controlling a hybrid brake system constructed by a regenerative brake apparatus and a hydraulic brake apparatus. This coordinated brake control system has been arranged to improve a fuel consumption by mainly operating the regenerative brake apparatus when a vehicle speed is higher than a predetermined vehicle speed and to decrease the regenerative braking torque while increasing the hydraulic braking torque as the vehicle speed is decreased. Further, a characteristic of the regenerative braking torque to be reduced is modified in response to a pressure difference between a master-cylinder hydraulic pressure and a wheel-cylinder hydraulic pressure so as to smoothly compensate for lack of the regenerative braking torque.
However, since this coordinated brake control system has been designed without taking account of a response delay of the hydraulic brake apparatus and a response delay of the regenerative brake apparatus, it is difficult to accurately control the hydraulic braking torque and the regenerative braking torque so as to accurately correspond the sum (total braking torque) of the regenerative braking torque and the hydraulic braking torque to a target total torque.
The applicant of the present invention has researched various methods for further smoothly varying a ratio between the regenerative braking torque and the hydraulic braking torque during a coordinated brake control while suppressing a fluctuation of the total braking torque actual value. Through the various researches, the inventors of the present invention have obtained a result that when a phase compensation is executed as to each of a hydraulic braking-torque command value and a regenerative braking-torque command value in addition to the control of U.S. Pat. No. 6,244,674, a fluctuation of the total braking torque actual value was not improved. The inventors have found that the pressure difference between the command value and the actual value of the wheel-cylinder hydraulic pressure includes an anticipated response delay, and this anticipated response delay has been already included in the phase compensation and is different from the control error and that even if the regenerative braking torque is directly corrected, a predetermined response delay will be generated until this correction is reflected in the actual regenerative braking torque.
Further, the inventors have reached a conclusion that the generation of the response delay is caused by correcting the regenerative braking-torque command value of a high-responsibility brake such as a regenerative brake apparatus on the basis of a difference between the command value and the actual value of the hydraulic braking torque, and that this problem is solved by correcting a regenerative braking-torque command value of a high-responsibility brake according to a difference between a reference model response value relative to the hydraulic braking-torque and an actual braking torque, where the reference model response value is obtained on the basis of a braking torque reference model which is determined upon taking account of a delay of a low-responsibility brake braking-torque relative to a torque command value of a low-responsibility brake such as a hydraulic brake apparatus.
It is therefore an object of the present invention to provide an improved coordinated brake control system which realizes the inventors"" invention discussed above.
An aspect of the present invention resides in a coordinated brake control system for a hybrid brake system of a vehicle. The coordinated brake control system comprising: a vehicle operating condition detector detecting a vehicle operating condition of the vehicle; a first brake generating a first braking torque according to a first braking torque command value; a second brake generating a second braking torque according to a second braking torque command value, a control responsibility of the first brake being higher than a control responsibility of the second braking torque; and a controller connected to the vehicle operating condition detector, the first brake and the second brake, the controller being arranged, to determine a total braking torque command value according to the vehicle operating condition, to distribute the total braking torque command value into the first braking torque command value and the second braking torque command value, to estimate the second braking torque, to calculate a reference model response value relative to the second braking torque command value on the basis of a braking torque reference model which is determined upon taking account of a delay of the second braking torque relative to the second braking torque command value, and to correct the first braking torque command value according to a braking torque difference between the estimated second braking torque and the reference model response value.
Another aspect of the present invention resides in a method of controlling a hybrid brake system of a vehicle, the hybrid brake comprising a first brake and a second brake whose control responsibility is not higher than a control responsibility of the first brake, the method comprises an operation of detecting a vehicle operating condition of the vehicle; an operation of determining a total braking torque command value according to the vehicle operating condition; an operation of distributing the total braking torque command value into a first braking torque command value according which the first brake generates a first braking torque and a second braking torque command value according which the second brake generates a second braking torque; an operation of estimating the second braking torque; an operation of calculating a reference model response value relative to the second braking torque command value on the basis of a braking torque reference model which is determined upon taking account of a delay of the second braking torque relative to the second braking torque command value; and an operation of correcting the first braking torque command value according to a braking torque difference between the estimated second braking torque and the reference model response value.
The other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.